Cathode ray oscillograph for recording transients



March 163943. s. READ, JR 2,313,967

CATHODE RAY OSCILLOGRAPH FOR RECORDING TRANSIENTS Filed Oct. 18,. 1959 2Sheets-Sheet 1 March 16, 1943. 55, READ, JR 2,313,967

CATHODE RAY OSCILLOGRAPH FOR RECORDING TRANSIENTS Filed Oct. 18, 1939 2Sheets-Sheet 2 Smaentor Otter Patented Mar. 16, 1943 CATHODE RAYOSCILLOGRAPH ron RECORDING TRANSIENTS Sidney Read, Jr., Haddonfield, N.J., assignor to Radio Corporation of America, a corporation of DelawareApplication October 18, 1939, Serial No. 300,035

13 Claims.

' incides with the application of a transient to be studied by means ofa spark discharge. Such a system is described in an article entitled Theuse of the high vacuum cathode ray tube for recording high speedtransient phenomena, by D. I. McGillewie, published in the October,1938, number of Electrical Communication. The single horizontal movementof the beam may be made to occur in a time varying between onemicrosecond and one millisecond, However,

since the horizontal deflecting voltage is proportional to the voltageacross a capacitor which is discharging through a resistor, theinstantaneous position of the beam with respect to time is not linear.It is the primary object of this invention, therefore, to provide adeflecting voltage which is linear with respect to time, which providesa single horizontal sweep of the cathode ray beam, and the time durationof which may be selected at will. I

In studying controlled transients, that is, transients which areproduced as the result of an operation which may be made to occur at anygiven time, it is desirable to initiate the cathode ray horizontaldeflection before the application of the transient to the verticaldeflecting plates. Where high speed transients are involved, that is,where the time required for the single excursion of the beam is measuredin microseconds, it

becomes exceedingly dificult to apply the transient at the correctinstant. As a result, the indication of the transient may appear at oneedge of the cathode ray screen, or it may even arrive after thehorizontal scanning operation has been completed. It is a further objectof this invention, therefore, to provide means for initiating thehorizontal scanning operation, or sweep, in a. first direction at afirst rate of speed, preferably at a relatively low speed so that thecontrolled transient may be applied to the vertical deflectingelectrodes to deflect thebeam in a second or trace indicating directionat a time when the beam has traversed but a small portion of itsscanning path. At the same time, in accordance with this invention, animpulse derived from the transient is utilized to change said rate ofspeed in said first direction, specifically to accelerate the horizontaldeflection of the beam to any desired degree so that the transientitself may be photographed or viewed on an enlarged time scale.

A further disadvantage common to all known devices of the prior art isthat the unit intensity of the light produced by the cathode ray beam isinversely proportional to the speed of the beam. That is, a brillianttrace is produced when the beam is moving slowly and a faint trace isproduced when the beam is moving rapidly. Transient phenomena usuallyinclude widely varying rates of change. by such transient phenomenavaries in amplitude in likeinanner. tion diflicult, and likewiseproduces photographic reproductions which are difficult to analyze.Unfortunately, it is usually the high speed transients that are of thegreatest importance, and it is these which are the most diflicult toreproduce, since they have the least amplitude. It is a further objectof this invention, therefore, to provide means for varying the beamintensity in proportion to the speed of vertical and horizontaldeflection so that the illumination of the trace produced by thetransient to be studied is constant throughout the curve.

Other objects, as well as a description of the nature and operation ofthis invention, will appear from a consideration of the followingspecification and the appended drawings.

Referring to the drawings, Figure l is a circuit diagram of a cathoderay oscillograph for indicating transient phenomena the occurrence ofwhich can be controlled; Figures 2 and Sam sketches illustrating theappearance of transients on a cathode ray screen; Figure 4 is thecircuit diagram of an embodiment of this invention in which thehorizontal deflection is accel-' erated by the applied transient; andFigure 5. is the schematic diagram of an embodiment of this. inventionin which the beam intensity is varied in proportion to the speed of thevertical and horizontal deflecting voltages; and Figures 5a and5b aremodifications of the invention of Figure 5. Similar reference numeralsrefer to similar parts throughout the several drawings.

Referring to Fig. 1, reference numeral 7 indicates a conventionalcathode ray tube having pairs of mutually perpendicular deflectingelectrodes 9 and H. One horizontal and one vertical deflecting electrodeand the No. 2' anode 53 are connected to ground. The cathode i5 is con-As a result, the trace produced This makes visual observaduced voltageacross the value by means of the nected to a suitable source ofpotential, supplied, for example, by means of a battery l1 and a shuntconnected resistor IS. The potential of the cathode is highly negativewith respect to ground. A slightly greater negative potential is appliedto the grid 2| through a switch 23. It will be recognized that theseconnections are entirelyconventional.

The transient voltage which is to be studied is Screen grid voltage forthe tube is derived from any suitable source, such as a resistor 35connected across battery 21, and its grid potential is determined bymeans of a potentiometer 31 connected across a source of voltage such asbattery 39 or the like. The cathode 4| of the pentode 33 is grounded,while the anode 43 is connected, preferably through a milliammeter 45,to the ungrounded terminal of capacitor 29. The anode 43 of tube 33 isalso connected to the remaining horizontal deflecting electrode 9through a battery 41, which has its negative terminal connected to thedeflecting electrode.

The operation of this device will now be described. The batterypotential is normally applied across capacitor 29 and the pentode 33. Inorder to prevent this positive voltage from deflecting the cathode raybeam ofi the screen, the series connected battery 41 is interposed inthe circuit to reduce the deflecting electrode to such a value that thebeam is normally located at a point near one edge of the fluorescentscreen. When the switch 3| is opened, the charging voltage is' removedfrom capacitor 29, which immediately begins to discharge through thepentode 33. It is known that the current through a pentode issubstantially constant over that range of its plate current-pla evoltage characteristic in which the plate voltage ezceeds the screenvoltage. The tube voltages are, therefore, selected to provide for itsoperation in this constant current region. As a result, the condenserdischarges at a rate which is linear with respect to time. Therecapacitor changes the potential of the horizontal deflectingelectrode, thus causing the beam to move in a horizontal direction. Whenthe condenser has' discharged the cycle is completed and the beamremains stationary. The beam therefore makes one excursion across thefluorescent screen at a linear rate.

The speed of deflection is determined by the bias which is applied tothe control grid of the pentode 33. This may be adjusted to any desiredgrid potentiometer 31. As indicated above, the plate and screen voltagesshould be made such that the beam velocity is linear with time over theuseful portion of the fluorescent screen. This is accomplished by makingthe plate voltage sufficiently high so that the beam traverses thescreen before the plate voltage has been reduced to a value comparableto that of the screen. The usual capacitanceresistance circut has anexponential discharge curve, since a resistor is not a constant currenteffective voltage on the graphic negative device in the presence of avarying terminal voltage.

The function of switch 23, connected in series with the cathode ray gridtube, is to shut off the beam during periods of preparation before thetransient is applied. When the switch is open, a high negative voltageis built up on the grid which effectually cuts ofi the beam. It has beenfound insufficient merely to-deflect the beam off the screen since thereis a certain amount of reflected illumination, due to reflection fromthe tube sidewalls, which tends to fog the photowhich is used to recordthe transient. Preferably the two switches 23 and 3| are operativelyconnected so that the proper bias is applied to the cathode ray grid notlater than the time at which the deflecting operation is begun. A thirdswitch 24, electrically connected to a transient source 26, may also beoperatively connected to the first named switches by means of which thetransient phenomena may be' instituted immediately after switches 3| and23 have opened and closed, respectively.

One difliculty with this arrangement is .best illustrated by referenceto Fig. 2, which represents a photograph of the sound track of thebeginning of the letter-I. This voltage was obtained by connecting amicrophone and audio frequency amplifier tothe input terminals 25. Itwill be observed that a portion of the screen between a and b has notbeen utilized. This is because of the difflculty of initiating thetransient which is to be studied immediately after the beam deflectionhas been instituted. The faster the occurrence of the transient, themore rapid the necessary beam deflection, and the more pronounced thisdifficulty becomes. A system for overcoming this disadvantage isillustrated in Fig. 4, to which reference is now made.

That portion of the device illustrated in Fig. 4 which includes thecathode ray tube 1 and its associated equipment, charging battery 21,capacitor 29, and the pentode 33, is identical to the correspondingportion ofthe device illustrated in Fig. 1. The change which is providedrelates to an automatic. means for accelerating the deflection of thebeam upon the application of the transient by causing the discharge of apair of gas tubes to change the bias on the grid of the pentode 33. Itwill be noted that a resistor 49 has been connected in series withresistor 35, between ground and the negative terminal of battery 21.This resistor provides a source of negative potential with respect toground for the normal bias of the pentode grid. A pair of gas dischargetubes 5| and 53, of the cold cathode type,

are connected in parallel and have their anode electrodes connectedthrough a switch 55 and a resistor 51 to the positive terminal ofbattery 21, and their cathode electrodes connected to the negativeterminal of battery 21 through a potentiometer 59. The gas tubes 5| and53' are provided with control electrodes'which are used to cause thebreakdown of the tubes upon the application of a suitable voltage. Thetubes 5| and 53 used by me in this arrangement are known as gas triodes,type OA4-G, described on page 45 of RCA Receiving Tube Manual RC-l i.The control electrodes 6| and 63 are connected, respectively, to theouter terminals of the secondary 65 of a transformer 61. The secondarycenter tap is connected through a switch 69 to a suitable source ofpositive potential, which may be supplied, for example. by means of avoltage regulator tube 1| and a potentiometer 13 sety, which are derivedfrom rially connected across battery 21. of transformer 61 transientthrough an amplifier 15.

The amplitude of the positive potential derived from potentiometer 13which is applied to thetwo control electrodes SI and 63 is adjusted tosuch a value that the tubes and 53 are just below their breakdown point.This permits one, or eventually both, of the gas tubes to becomeconductive when potentials of the proper polarithe applied transient,are applied to the respective control electrodes. In the absence of sucha voltage, and prior to the breakdown of the tubes 5| and 53, there isno voltage drop in potentiometer normal operating potential ofthegrid ofpentode 33 is determined by the adjustment of potentiometer 31.'I'hispotential will be negative with respect to ground and will. beselected to provide any desired initial rate of horizontal deflectionfor the cathode ray tube 1. Upon the application of a transient voltage,the subsequent breakdown of at least one of the gas tubes 5| and 53produces a voltage drop in potentiom- The primary is,energized by theapplied a circuit which may include eter 59 which causes the grid ofpentode 33 to become more positive with respect to ground. The currentflowing in potentiometer 59 is practically the same Whether one or bothtubes break down, as gas tubes maintain essentially a constant voltage.The amplitude of the grid potential is suitably selected to provide anydesired rate of deflection for the remainder of the cycle. Switches 69and 55 are included in the circuits shown to remove the potentials fromthe gas tubes 5| and 53 after the observation or recording has beenmade, to extinguish the tubes and to prepare the device for a subsequentobservation.

The method of using this device is similarto that of the embodimentdescribed in Fig. 1.

Switch 3| is opened and the cathode ray beampermitted to begin itshorizontal deflection at a low rate, and then at the proper instant thetransient is applied and the observation made with the desiredaccelerated time displacement of the beam.

By means of the meter 45, which indicates the amplitude of the dischargecurrent, it is D0551?- ble to predetermine the velocity of the beamdeflection. The beam velocity V in inches per sec- 0nd is expressed bythe equation I V- Xl0 where I=current in milliamperes, C=capacitance ofcapacitor in microfarads, and S=volts required to deflect the beam oneinch 4 across the screen. Fig. 3 illustrates the improved operation ofthe system which has been described immediately above. The distance cdillustrated in the figure is that distance through which the beam movesat the initial slow rate of speed, prior to the application of thetransient voltage. The transient voltage itself, however; byaccelerating the horizontal deflection of the beam, is viewed on anaccelerated time base covering the region d-e. It is no longer necessaryto view the transient voltage with a low horizontal deflecting speed,since by the arrangement shown the transient voltage may readily beapplied at the propbeen initiated.

59 so that the It will be realized that the photographic image of thatsection of the horizontal trace H which is made prior to the applicationof thetransient voltage is very dense. This density is caused by twofactors. The amount of light emitted per unit area from a fluorescentscreen is a function 'of the beam velocity, so that more light isproduced in the initial region in which the beam moves comparativelyslowly. In addition, the exposure of a photographic negative is afunction of the amount of light falling thereon. These factorsheretofore have caused considerable difliculty in recordingoscillograms. When the intensity of the beam is sufliciently great for aproper illumination during the time of rapid beam deflection, a decreasein deflection rate results in overexposure and in some cases in burningof the screen.

A modification of this invention is illustrated in Fig. 5 whichcompletely overcomes this o'bjection by providing means for varying thebeam intensity in proportion to the horizontal and vertical deflectingspeed. This part of my invention has wide application to all types ofmechanical as well as cathode ray oscillographs. It'may be ly assistsvisual observation of voltage peaks which are usually indistinctlyreproduced by reason of the high velocity of the beam.

Referring to Fig. 5, a cathode ray tube 1 is utilized, as before.Operating potentials for the tube are supplied by a. source of voltage11 and a voltage divider l9. An initial operating grid bias is suppliedby an adjustable connection 17 to the voltage divider I 9 through a pairof grid leak resistors 1'9 and 8|."The amplitude of this bias ispreferably sufiicient to shut off the cathode ray beam.

As before, the input voltage is applied between the two verticaldeflecting electrodes ll in this case, however, the time delay network83 is included in the input circuit for reasons which will be pointedout hereinafter.

In order to provide automatic control of the beam intensity, two controlcircuits have been provided which apply to the control grid 2| positivepotentials which are proportional, respectively, to the rate of changeof horizontal and vertical deflecting voltages. The horizontaldeflecting control is obtained by connecting the primary of atransformer 85 in series with the capacitor 29 which is used, as before,to produce a linear deflection of the cathode ray beam in superimposedvoltage is also proportional to the I rate of horizontal deflection.

The control voltage for maintaining constant unit illumination duringvertical displacement of the cathode ray beam is controlled by a circuitwhich includes a transformer 81 and pushpull rectifiers 89 and 9!. Theprimary of transincludes a pair of small capacitors 93 and 95 and aresistor 91, the midpoint of which is connected to the adjustablecontact H. The outputs of the two rectifiers 89 and 9| are connected tothe common point of resistors 19 and BI, so that the control voltagedeveloped in response to the applied input voltage is effectivelyconnected in series with the normal grid bias. The rectifier circuitshown produces a unipotential output voltage from an alternating inputvoltage. A transient of either polarity, therefore, will cause thecontrol grid 2| to become more positive. As a result, the cathode raybeam intensity is increased by an amount which is proportional to therate of change of the applied transient without regard to its polarity.The unit illumination of the cathode ray trace is therefore constant asthe vertical deflecting speed varies.

In order to make the device fully automatic, the switch which was thehorizontal beam deflection has been replaced by a resistor 99. The valueof resistor 99 is preferably high with respect to the impedance ofpentode 33 during any part of the useful period of conductivity of thelatter. The purpose of resistor 99 is to charge capacitor 29, whilepentode 33 discharges the capacitor at a linear rate, as before. It istrue that the presence of the charging resistor 99 during the dischargecycle tends to make the deflecting voltage slightly non-linear. This canbe overcome by replacing resistor 99 by a constant current device suchas a pentode 99a of Figure a, or a vacuum phototube 99b of Figure 5bwith suitable means for illuminating the same.

The circuit for applying a more positive bias to the control grid ofpentode 33 in response to the applied transient voltage, includingtransformer 61 and the gas tubes 51 and 53, is the same as thatdescribed in connection with the preceding circuits and need not beexplained again in detail. However, it is desirable to point out thatthe applied transient initiates the horizontal deflection of the cathoderay a brief interval before the same transient is applied to thevertical deflecting electrodes by reason of the interposition of thetime delay network 83. The degree of the delay required depends upon thetime necessary for one or both of the gas tubes to become conductive.This time is of the order of microseconds, and for any but exceptionallyrapid transients, probably need not be considered. The input circuitsshown include iron cored transformers; however, other coupling means maybe preferable for high speed transients.

It will be recalled that in the arrangement illustrated in Fig. 4 theinitial bias of the grid of tube 33 was adjusted to that value whichwould produce the desired initial horizontal rate of deflection. In thepresent arrangement, however, the initial bias is adjusted to a valuewhich reduces the p ate current of the pentode 33 to a minimum. The sameamount of current flows in 99, thereby maintaining an equilibriumvoltage across capacitor 29. The position of the arm of potentiometer 31and the potential of batterv 81 therefore determine the initial positionof the beam along the horizontal axis. In the device illustrated inFig.5, it is no longer necessary to provide the initial slow deflection,

servation, it is necessary since the device is completely automatic, andthe applied transient voltage itself initiates the horizontal deflectingoperation at a fixed predetermined time before the application of thevoltage to the vertical deflecting electrodes.

As in the preceding arrangements, the device illustrated in Fig, 5produces but a single cycle of operation upon the application of atransient voltage. To prepare the device for a second obto open circuitswitches 55 and 69, thus' removing the anode potential from gas tubes 5|and 53, restoring the initial potential on the grid of pentode 33, andpermitting capacitor 29 to become recharged. The circuit includingelements 29 and 85 inherently serves to diminish the beam on the returnpath in case of a resetting operation by means of opening switches 55and 69.

previously used to initiate With respect to the adjustment of theinitial negative bias on the control grid 2| of the cathode ray tube 1,the amplitude of this voltage is adjusted to that value whichextinguishes the cathode ray beam. This original bias is overcome,however, upon the application of a vertical or a horizontal deflectingvoltage. Consequently, the cathode ray beam impinges on the fluorescentscreen only when deflecting voltages are also present. This preventsburning of the screen during periods when no deflecting voltages areapplied, and also completely removes any illumination during the sameperiods. This greatly facilitates photographing the effect of thetransients, since there is no stray illumination to fog the negative Ihave thus described an improved cathode ray oscillograph having certainnew features which are also applicable to other types of oscillographs.Of general application is the arrangement by which the beam intensity iscontrolled in accordance with the rates of speed of the horizontal andvertical deflections. Of particular importance to the study of highspeed transient phenomena are the linear deflecting voltage arrangement,the horizontal deflection accelerating system, and the automatic systemfor scanning a non-recurrent transient.

I claim as my invention:

1. A device'of the character described comprising a cathode ray tubehaving vertical and horizontal beam deflecting means and a beamintensity control electrode normally biased to shut off said beam; asource of voltage for applying a single deflecting impulse to saidhorizontal deflecting means, said source comprising a capacitor, circuitconnections between said capacitor and said horizontal deflecting means,a source of positive potential, switching means for normally connectingsaid source across said capacitor for charging said capacitor, athermionic tube having a substantially constant plate voltage-platecurrent characteristic connected across said capacitor for dischargingsaid capacitor at a constant rate when said switching means is operatedto disconnect said source from said capacitor, the instantaneousposition of said beam being proportional to the instantaneous voltageacross said capacitor; other switching means in circuit with saidcontrol electrode and operatively connected to said first switchingmeans for applying an operating bias to said electrode, and means forapplying a voltage to be indicated to said vertical deflecting meansimmediately after said switches have been operated;

2 In a device of the character described for indicating a voltage trace,a cathode ray tube having vertical and horizontal beam deflecting means;means for energizing said horizontal defleeting means to cause said beamto move horizontally in a given direction at a predetermined rate priorto the impression of said voltage; means for subsequently energizingsaid vertical beam deflecting means in accordance with said voltage tobe indicated; and means responsive to said last named voltage forcausing said beam to complete its movement in said direction at adifferent rate.

3. In a device of the character described for indicating a transientvoltage trace, cathode ray beam producing means; means for initiallysweep-deflecting said beam in a first direction at a first rate of speedin the absence of an impressed transient voltage; means for subsequentlydeflecting said beam in a second or trace indicating direction inaccordance with an impressed transient voltage; and means responsive tosaid last named means for substantially changing the rate of speed ofsaid beam in said first direction.

4. In a cathode ray oscillograph device having beam producing means forindicating transient voltage traces, sweep voltage responsive means forinitially deflecting said beam in a given sweep direction at apredetermined rate of speed in the absence of impressed transientvoltages to be indicated, voltage responsive means for subsequentlydeflecting said beam in a trace indicating direction in accordance withan impressed transient voltage, and means responsive to said transientvoltage for causing said beam to continue in the same sweep direction ata substantially increased rate of speed.

5. In a device of the character described, a

variable impedance device; cathode ray beam producing means; means fordeflecting said beam in a first direction at a rate of speed determinedby said variable impedance device; means for deflecting said beam in asecond direction in ac-. cordance with a voltage which is to beindicated; and means responsive to said voltage for varying theimpedance of said device to change the speed of deflection of said beamin said first direction. 6. In a device of the character described, acapacitor, means for charging said capacitor, a variable impedancedevice for discharging said capacitor; an indicating screen; cathode raybeam producing means; means for deflecting said beam across said screenin a-first direction at a rate of speed determined-by the initialimpedmce of said device; means for deflecting said ream in a seconddirection across said screen in accordance with a voltage which is to beindizated; and means responsive to said voltage for :hanging theimpedance of said device to change ;he speed of deflection of said beamin said first iirection.

'7. A device of the character described com-" rising a cathode ray tubehaving vertical and iorizontal beam-deflecting means and a control:lectrode; a voltage source for applying a delecting impulse to saidhorizontal deflecting means, said source comprising a capacitor, meansor charging said capacitor, and means for dis- :harging said capacitorat a given instant and it a constant rate, the position of said. beameing proportional to the instantaneous voltage .cross said capacitor,and circuit connections beween said capacitor and said control electrodeIhereby the intensity of said beam is determined y the rate of dischargeof said capacitor.

8, A device of the character described comprising a cathode ray tubehaving vertical and horizontal beam-deflecting means and a controlelectrode, a voltage source for applying a single deflecting impulse tosaid horizontal deflecting means, said source comprising a capacitor,means for charging said capacitor, and means for discharging saidcapacitor at a given instant and at a constant rate, the position ofsaid beam being proportional to the instantaneous voltage across saidcapacitor, and circuit connections between said capacitor and saidcontrol electrode whereby the intensity of said beam is varied by therate of discharge of said capacitor, means for applying a voltage to beindicated to said vertical deflecting means, and means for varying theintensity of said beam in accordance with the rate of change in saidvoltage to be indicated.

9. A device of the character described comprising a cathode ray tubehaving vertical and horizontal beam deflecting means, means for applyinga deflecting impulse to said horizontal deflecting means for deflectingsaid beam at a first rate, means for applying a voltage to be indicatedto said vertical deflecting means, means responsive to said voltage forchanging the horizontal rate of deflection to a second rate, means forcontrolling the intensity of said beam as a function of the rate ofchange of said horizontal deflecting impulse, and means for alsocontrolling the intensity of said beam as a function of the rate ofchange of said voltage to be indicated.

10. A device of the character described comprising a cathode ray tubehaving vertical and horizontal beam deflecting means, a voltage sourcefor applying a single deflecting impulse to said horizontal deflectingmeans, said source comprising a capacitor, means for charging saidcapacitor, means including current-responsive means in circuitwith saidcapacitor for discharging said capacitor at a substantially con stantrate, said current-responsive means being coupled to said cathode raytube so as to control the intensity of said beam, the position ofsaidbeam being proportional to the instantaneous voltage across saidcapacitor, and the intensity of said beam being varied by the rate ofdischarge of said capacitor through said currentresponsive means.

11. In a device of the character described, a capacitor, a source ofvoltage for charging said capacitor, a constant current thermionic tubeconnected in parallel with said capacitor for discharging saidcapacitor, means for applying a grid bias to said tube forcontrolling-the normal rate of discharge of said capacitor, a cathoderay tube having vertical and horizontal deflecting electrodes,connections from said capacitor to said horizontal deflectingelectrodes, the horizon tal position of said ray being proportional tothe charge on said'capacitor, means for applying a voltage to beobserved to said vertical deflecting electrodes, and means responsive tosaid voltage for changing said grid bias to increase the rate ofdischarge of said capacitor 12. A device of the character described inclaim 11 which includes means for delaying the application of saidvoltage to said vertical deflecting electrodes so'that said cathode rayis not deflected vertically before the rate of discharge of saidcapacitor has been increased.

13. In a device of the character described, a capacitor, a source ofvoltage for charging said capacitor, a constant current thermionic tubeconnected in parallel with said capacitor for discharging saidcapacitor, bias means for applying tube having vertical and horizontaldeflecting electrodes, means coupling said capacitor to said horizontaldeflecting electrodes whereby the horia grid bias to said tube todetermine the normal rate of discharge of said capacitor, a cathode rayfleeting electrodes, a gas-filled grid control tube coupled to saidinput means and in circuit with said bias means whereby said voltage tobe observed causes said gas-filled tube to become conductive to'changethe grid bias of said constant current tube.

SIDNEY READ, JR.

